A wide variety of processes use co-current flow reactors, where a fluid or fluids flow over a solid bed of particulate materials, to provide for contact between the fluid and solid particles. In a reactor, the solid may comprise a catalytic material on which the fluid reacts to form a product. The fluid can be a liquid, vapor, or mixture of liquid and vapor, and the fluid reacts to form a liquid, vapor, or a mixture of a liquid and vapor. The processes cover a range of processes, including hydrocarbon conversion, gas treatment, and adsorption for separation.
Co-current reactors with fixed beds are constructed such that the reactor allows for the fluid to flow over the catalyst bed. When the fluid is a liquid, or liquid and vapor mixture, the fluid is usually directed to flow downward through the reactor. Multibed reactors are also frequently used, where the reactor beds are stacked over one another within a reactor shell. Typically, they are stacked with some space between the beds.
The interbed spaces are often created to provide for intermediate treatment of the process fluid, such as cooling, heating, mixing and redistribution.
In exothermic catalytic reactions, the control of fluid temperature and distribution is important. The temperature and composition of the fluids from an upper catalyst bed and from outside of reactor should be well mixed before being distributed to the lower catalyst bed. Initial poor temperature and composition distribution at top of a catalyst bed can persist or grow as the process fluids move down the reactor. Hot spots can develop and cause rapid deactivation of the catalyst and shorten the reactor cycle length. The space between catalyst beds is for the injection of a quench gas or liquid and for fluid mixing and distribution. In hydrocarbon processing, the quench gas is often a cool hydrogen/hydrocarbon stream. However, cooling a fluid without controlling the mixing and distribution leads to uneven reactions and uneven temperature distribution in subsequent reactor beds. And complex mixing and distribution systems takes up valuable space in a reactor chamber holding multiple catalyst beds.
Due to constraints in the height of the space between reactor beds, there is a limited amount of space for introducing a quench fluid and mixing the vapor and liquid along with the quench fluid. Particularly, for existing hydroprocessing reactors, the space between catalyst beds is already set, and sometimes it is difficult to install new internals for improving mixing of fluids within the existing interbed space without reducing the height of catalyst beds. Even for new reactors, it is often desired to reduce the overall size of the reactors to reduce capital expenditure and the profile of the reactor in a processing plant. Therefore, it is desirable to provide for good mixing of fluids between adjacent catalyst beds in a relatively short interbed space.
Previous attempts to overcome these limitations have included vortex or turbulent type mixers which generally include providing flow of the fluids together in a manner to affect mixing. An example of a vortex type mixer is described in U.S. Pat. No. 8,017,095. The cylindrical mixing device 40 is positioned on a collecting tray and includes inlets 50 and 55 and a single outlet 80 in the bottom center of the bottom wall. The fluid and liquid enter the device together through inlets 50 and 55. These devices are limited in that mixing is affected by the turbulent or swirling flow of fluids together within the device in the same general direction and with vapor atop of liquid.
The design of reactor internals to overcome these limitations can save significantly on the valuable space within a reactor. New reactor internals that improve the utilization of the space within a reactor shell can maximize catalyst loading, and obviate the need for new reactor shell components, as well as prevent the down time for replacing an entire reactor.